Present study is in progress since 1990-91 at Crop Research Centre of G. B. Pant University of Agriculture and Technology, Pantnagar, U.S.Nagar (Uttaranchal) to study the long term effects of herbicide use in rice-wheat system. Treatments consisted of combinations of butachlor at 1.5 kg ha-1,hand weeding (30 and 60 days after transplanting) and weedy check in rice and each kharif season treatment followed by isoproturon at 1.0 kg ha-1,hand weeding twice (30 and 60 days after sowing) and weedy check in wheat. Experiment was laid out in randomized block design, with nine treatments and three...